I. Field of the Invention
This invention relates to processes for making cheese and to cheese products so made. More particularly, the invention relates to the use of ripening aids employed in processes for making Cheddar cheese.
II. Description of the Prior Art
The manufacture of Cheddar cheese is carried out on a large scale in many countries. Very briefly summarized, the traditional manufacturing process involves coagulating milk to form solid curds and liquid whey, separating the curds from the whey, treating the curds to form a Cheddar cheese product and aging (i.e. so-called "ripening") the cheese product under controlled temperature conditions to allow the desired taste and texture to develop. If the aging or ripening period is short, the product is known as "mild" Cheddar. Longer aging periods lead to the production of "medium", "old" and "very old" Cheddars. The longer the aging period, the more the "sharp" or "tangy" taste develops, and the more valuable is the resulting cheese. A more complete description of cheese making in general, and Cheddar cheese making in particular, can be found in an article by Frank V. Kosikowski published in the Scientific American, Vol. 252(5), 1985, pp. 88 to 99. The disclosure of this article is incorporated herein by reference.
The production of Cheddar cheese in large quantities has recently encountered several problems. Firstly, while the "old" and "very old" Cheddars command a higher price in the marketplace, they are expensive to produce because of the storage and refrigeration costs required for the lengthy ripening process, which can involve up to three years of storage at a temperature of about 10.degree. C.
Furthermore, the coagulant traditionally employed for coagulating the milk is "calf rennet", i.e. an enzyme extract from the stomachs of young, milk-fed calves. Because of a recent reduction in the number of calves being slaughtered and an increased demand for cheese, calf rennet has increased significantly in price in recent years. Alternative coagulants, i.e. so-called rennet substitutes, are known and used on a large scale, e.g. porcine pepsin, bovine pepsin and Mucor miehei protease, but they do not facilitate the ripening process in Cheddar cheese manufacture as effectively as calf rennet. As a result, they are commonly employed only for the production of mild Cheddar cheese. Taking porcine pepsin as an example, this rennet substitute is unstable at the pH values and temperatures employed during the "cheddaring" step of the process and, as a result, the Cheddar ages very slowly compared to Cheddar prepared with calf rennet.
A further problem encountered by Cheddar cheese producers is that the use of raw (unpasteurized) milk is discouraged or banned by many regulatory agencies because of the risk that pathogenic bacteria in the raw milk may contaminate the cheese product. However, the use of pasteurized or partially pasteurized milk as the starting material has an effect on the ripening process because certain bacteria present in raw milk apparently affect the process of flavour development. Thus, longer ripening periods are required than when raw milk is employed.
The ripening period cannot be reduced by increasing the temperature at which the product is stored because of possible flavour defects and because of the accompanying risk of spoilage of the cheese. Accordingly, attempts have been made to provide cheese ripening aids, i.e. materials that can be added to the milk starting material or to the cheese product to decrease the ripening period without adversely affecting the flavour and texture of the cheese. A limited number of products are available commercially as cheese ripening aids, e.g. .beta.-galactosidase (sold by G. B. Fermentations under the trade mark Maxilact), and there are reports of accelerated ripening by the use of microbial proteases, e.g. B. subtilis neutral protease, Aspergillis orryzae acid protease, B. licheniformis alkaline protease, and K. lactis proteases, and by the use of Streptococcus lactis mutants and microbial lipases. However, commerical proteases having a high ratio of endo- to exo-peptidase activity tend to cause excessively gross proteolysis leading to abnormal body/texture development and some cause a bitter off-flavour in the aged cheese. The efficacy of .beta.-galactosidase as an accelerator of cheese ripening has, moreover, been questioned in the scientific literature (Advances in the Microbiology and Biochemistry of Cheese and Fermented Milk, by B. A. Law, 1984, Elsevier Applied Science, p. 218).
There is accordingly a need for a more effective cheese ripening aid for use in the manufacture of Cheddar cheese.